I have an Android app on Java that use the Volley library. I’m taking over the work of a former intern who make a RequestUtils class to create his own requests. I need to upgrade his work in order to make a more reliable app and I read a lot of documentation to know the best practices.

I need to get the user informations from my server to display it in my Activity, and if there is an error make a Toast. I use ViewModel to avoid HTTP request at each rotation change or whatever, and currently it’s the best for me if there is a request in the case of the Activity being entirely recreate because of the phone killing it in the background.

I’m at the point that I have a UserViewModel class and UserRepository class, and in this Repository class I want to use the request that he made for that, except that I don’t know the best way (I have 3 different solutions at the moment) to pass the VolleyError to the ViewModel if there is any.

I also want to remind that is not a best practice to have a LiveData in a Repository class.

There is some code that I have.

RequestUtils.java getUser :

public static void getUserInfos(Response.Listener<User> responseListener, Response.ErrorListener errorListener) {
        GsonRequestByClass<User> gsonRequest = new GsonRequestByClass<>(Request.Method.GET, STRING_URL + "users/" + ID, User.class, responseListener, errorListener);
        HTTPRequest.getInstance().addToQueue(gsonRequest);
    }

The method is currently called in the onCreate method of my MainActivity.java, I want to use it in my UserRepository:

import static com.example.app.utils.RequestsUtils.getUser;

public class MainActivity extends AppCompatActivity {
    //...
    User user;
    
    //...
    protected void onCreate(Bundle savedInstanceState) {

        //BEFORE
        getUser(new Response.Listener<User>() {
                    @Override
                    public void onResponse(User response) {
                        user = response;
                        //do smth
                    }
                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        //There is a Toast here
                    }
                });

        //NOW
        UserViewModel userModel  = new ViewModelProvider(this).get(UserViewModel.class);
        userModel.getUser1().observe(this, userResp->{
            user = userResp;
            //do smth
        }); //how to handle error ?
    }
}

UserViewModel.java

public class UserViewModel extends ViewModel {
    private UserRepository userRepository;

    private MutableLiveData<User> userLiveData;

    public UserViewModel(){
        userRepository = new UserRepository();
    }

//solution 1
    public LiveData<User> getUser1() {
        if (userLiveData == null){
            if (!userRepository.retrieveUserInfo1()){
                userLiveData = new MutableLiveData<>();
                userLiveData.setValue(userRepository.getUser());
            } else {
                //how indicate that there is an error for the Toast in activity ?
            }
        }
        return userLiveData;
    }

//solution 2
     public LiveData<User> getUser2() {
        if (userLiveData == null){
            Response<User> reponse = userRepository.retrieveUserInfo2();
            if (reponse.isSuccess()){
                userLiveData.setValue(reponse.result);
            } else {
                //make smth with response.error
            }
        }
        return userLiveData;
    }

//solution 3
    public LiveData<User> getUser3() {
        if (userLiveData == null){
            try {
                userLiveData = userRepository.retrieveUserInfo3();
            } catch (VolleyError e) {
                throw new RuntimeException(e);
            }
        }
        return userLiveData;
    }

}

UserRepository.java

public class UserRepository {
    private User user;
    private boolean errorReq;
    Response<User> responseReq;

    public User getUser(){
        return user;
    }


//solution 1
    public boolean retrieveUserInfo1() {
            getUserInfos(new Response.Listener<User>() {
                @Override
                public void onResponse(User response) {
                    user = response;
                    errorReq = false;
                }
            }, new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    errorReq = true;
                }
            });
        return errorReq;
    }


//solution 2
    public Response<User> retrieveUserInfo2() {
                getUserInfos(new Response.Listener<User>() {
                    @Override
                    public void onResponse(User response) {
                        responseReq = Response.success(response, null);
                        user = response;
                    }
                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        responseReq = Response.error(error);    
                    }
                });
            return responseReq;
        }

//solution 3
     public Response<User> retrieveUserInfo3() throws VolleyError {
                getUserInfos(new Response.Listener<User>() {
                    @Override
                    public void onResponse(User response) {
                        errorReq = false;
                        user = response;
                    }
                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        errorReq = true;
                    }
                });
            if (errorReq){
                throw new VolleyError();
            }
            return user;
        }

}

If anyone can help me ! This is my first question on SO, I hope I write it correctly and explain it well, tell me otherwise.